Certain conditions and diseases can be indicated by analyzing exhaled air. For instance, air exhaled by persons suspected to be infected by the pathogenic bacteria Helicobacter pylori is analyzed by a variety of methods. According to one such method used clinically for a number of years, the patient is made to swallow an isotope-labelled urea preparation, in particular a preparation containing .sup.14 C or .sup.14 C labelled urea. Helicobacter pylori present in the gastrointestinal tract produces enzymes degrading the urea to ammonia/carbon dioxide. The gastro-intestinally formed carbon dioxide is transported to the lungs through the normal physiology of the body and exhaled together with other carbon dioxide formed by the body. The exhaled carbon dioxide is trapped by a suitable liquid, for instance, aqueous sodium hydroxide, which is examined with the aid of appropriate measuring instruments, for instance scintillation counters for detecting radioactive decay of .sup.14 C.
The methods known in the art are relatively complicated and time consuming, and require the use of expensive and bulky apparatus. The provision of simple and cheap methods for use in decentralised health care has still not been adequately solved. There is thus a need for such methods and corresponding devices.